Spring boot throwing null pointer exception while using Spring data JPA

I am a newbie to spring, when I am trying to save an entity to the database it is throwing a null pointer exception. Here is the relevant code for reference:-

Here is the controller:-

import com.project.newsblog.entities.Post;
import com.project.newsblog.service.PostService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class MyController {
    @Autowired
    public PostService postService;


    @PostMapping(value = "/post")
    public String post(@RequestBody Post item){
        System.out.println(item.toString());
        postService.post(item);
        return "Successful";
    }

}

Here is the service Service(root cause of the eror):-

import com.project.newsblog.entities.Post;
import com.project.newsblog.repository.PostRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class PostService {

    private PostRepository postRepository;

    public List<Post> getAllPost(){
        return postRepository.findAll();
    }
    public void post(Post post){
        postRepository.save(post);
    }
}

Here is the Entity for reference:-

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import java.time.LocalDateTime;

@Entity
public class Post {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;
    private String creator;
    private  String title;
    private String text;
    private LocalDateTime dateTime;

    public Post() {
    }

    @Override
    public String toString() {
        return "Post{" +
                "id=" + id +
                ", creator='" + creator + '\'' +
                ", title='" + title + '\'' +
                ", text='" + text + '\'' +
                ", dateTime=" + dateTime +
                '}';
    }

    public Post(String creator, String title, String text) {
        this.creator = creator;
        this.title = title;
        this.text = text;
        this.dateTime = LocalDateTime.now();
    }

    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public String getCreator() {
        return creator;
    }

    public void setCreator(String creator) {
        this.creator = creator;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getText() {
        return text;
    }

    public void setText(String text) {
        this.text = text;
    }

    public LocalDateTime getDateTime() {
        return dateTime;
    }

    public void setDateTime(LocalDateTime dateTime) {
        this.dateTime = dateTime;
    }
}

There seems to be a problem while saving the json payload to database. I think I am missing something which I am not able to figure out. Please help me out. Here's the most relevent debug message:-

Post{id=1, creator='Someone', title='This is the title', text='This is the title', dateTime=null}
2021-06-15 22:52:22.145 DEBUG 14756 --- [nio-8080-exec-8] o.s.web.servlet.DispatcherServlet        : Failed to complete request: java.lang.NullPointerException
2021-06-15 22:52:22.146 ERROR 14756 --- [nio-8080-exec-8] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause

java.lang.NullPointerException: null
    at com.project.newsblog.service.PostService.post(PostService.java:20) ~[classes/:na]
    at com.project.newsblog.controller.MyController.post(MyController.java:21) ~[classes/:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:564) ~[na:na]

Edit:- When I am annotating PostRepository line in service part with @Autowired, it is giving the error: "No qualifying bean of type 'com.project.newsblog.repository.PostRepository'". Here is the repository code:-

package com.project.newsblog.repository;

import com.project.newsblog.entities.Post;
import org.springframework.context.annotation.Bean;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;


@Repository
public interface PostRepository extends JpaRepository<Post, Long> {
}